A common method for the treatment of municipal and plant sewage wastes is the activated sludge process in which large numbers of microorganisms are present, and, in fact, necessary, to treat the sewage. Such systems generally comprise a rapid flocculation of the materials in the biomass followed by their entrapment and subsequent settling and the reduction of the sludge liquor Biological Oxygen Demand (B.O.D.).
One problem, however, has been the disposal of the waste activated sludge. Not all of it can be returned to the above-described process. This is further complicated by the fact that the activated sludge, containing as it does large numbers of organisms of which apparently the genus Zoogloea seems to predominate, is very difficult to dewater because of the water-retention properties of the polysaccharides and other polymeric materials that are part of the capsular material surrounding the microorganic cells. As a consequence, the sludge is slimy and it is not possible to readily dewater such sludges to build up high solids materials that can be readily disposed of. In addition, the sludges after the limited dewatering heretofore possible, still give off unpleasant odors limiting their use or mode of disposal.
Efforts to treat activated sludge to facilitate the dewatering have included heat treatment. This has not proven satisfactory in that such heating usually results in solubilization of some of the sludge solids so that the resulting liquor produced has a high B.O.D. and has to be further treated before it can be discharged to a watercourse.
Other efforts have involved adding materials to the activated sludge, such as fly ash, and using this as a means to trap the solids to obtain liquors having a low B.O.D. This is expensive in terms of materials and energy involved in compressing the resulting mass and, further, still does not result either in a high solids material or a liquor with a sufficiently low B.O.D.